operator_enum of object.mesh_add and object.empty_add is displayed unexpected
I've found the solution:

The API has been changed (Code from /usr/share/blender/scripts/startup/bl_ui/space_view3d.py):

class INFO_MT_mesh_add(Menu):
    bl_idname = "INFO_MT_mesh_add"
    bl_label = "Mesh"

    def draw(self, context):
        from .space_view3d_toolbar import VIEW3D_PT_tools_add_object

        layout = self.layout

        layout.operator_context = 'INVOKE_REGION_WIN'

        VIEW3D_PT_tools_add_object.draw_add_mesh(layout)


I was misleaded by this comment in INFO_MT_add:

#layout.operator_menu_enum("object.mesh_add", "type", text="Mesh", icon='OUTLINER_OB_MESH')


This code doesn't work anymore!